How to identify if concrete blocks are 5N or 7N ?

[dave_104]

Hi,

As per subject, how can I tell if some blocks I have here in a wall are 5N or 7N? They've been in place for maybe 30/40 years and ones I've taken out weigh about 18Kg each. I do know that 5N blocks aren't a new thing, but how can I identify the difference?

Thanks
Dave

 

[blup]

The experts on here will identify it from your pics

 

[stevie888]

They sound like conventional concrete rather than Celcon type ligtweight so I would expect at least 7N.

Why do you need to know?

 

[stuart45]

I can't remember ever laying a 5N block.

 

[dave_104]

Why do you need to know?

Thanks for that, an online structural engineer is asking as we're wanting to attach a beam to the wall. If the blocks are not 7N then it seems the building codes require a spreader plate which would be very troublesome to install.

 

[dave_104]

####
I'll close this question off now as the structural engineer has worked on assuming the blocks are just 3.6N types, and this calculates sufficient for hanging the beam, so I don't need to know about the blocks now and not sure if anyone else does.
Thanks for your replies BTW!
####

 

[Koolpc]

Hi,

As per subject, how can I tell if some blocks I have here in a wall are 5N or 7N? They've been in place for maybe 30/40 years and ones I've taken out weigh about 18Kg each. I do know that 5N blocks aren't a new thing, but how can I identify the difference?

Thanks
Dave

View attachment 408077

My mate usually gets his mother in law to head butt them...

 

[stevie888]

Thanks for that, an online structural engineer is asking as we're wanting to attach a beam to the wall. If the blocks are not 7N then it seems the building codes require a spreader plate which would be very troublesome to install.

Safe but lazy TBH.

 

[^woody^]

Thanks for that, an online structural engineer is asking as we're wanting to attach a beam to the wall. If the blocks are not 7N then it seems the building codes require a spreader plate which would be very troublesome to install.

The fact that the blocks are hollow may be more pertinent than the compressive strength and even if 7N, may still require increased padstone, larger spreader plate or localised rebuilding with either solid blocks or filled voids.

Make sure your engineer has factored hollow blocks in.